Effect of aqueous environments on the fatigue behavior of 90-10 copper nickel
Fatigue tests on compact tension specimens of 90-10 copper nickel were conducted in 3.5% NaCl solutions. Anodic or cathodic currents were applied during testing. Anodic currents decreased and cathodic currents increased the fatigue life. Both anodic and cathodic currents changed the fracture mode from predominantly transgranular to intergranular. Constant extension rate tests were performed on similar CT specimens in environments of 3.5% NaCl solution and 3.5% NaCl solution titrated to pH 1.0 with various levels of applied current. The environment had little influence on the monotonic failure of 90-10 copper nickel. Polarization studies were conducted to determine the effects of welding and pH on the corrosion behavior of 90-10 copper nickel. The rate of corrosion was less in the weld and the heat affected zone than in the base metal. As the pH of the environment was lowered, the corrosion rate of 90-10 copper nickel increased due to the retardation of film formation and repassivation.
These studies showed that three different mechanisms of corrosion fatigue were likely: localized anodic dissolution, surface film rupture and hydrogen embrittlement. The dominance of one mechanism over the other two depends on the applied current. No evidence of susceptibility to stress corrosion cracking was found, therefore, a true corrosion fatigue process is operative in 90-10 copper nickel.